The overall objectives of this study are (1) determination of the control elements (genetic and biochemical) for regulation of aminoacyl-tRNA synthetase formation in both E. coli and S. typhimurium, and (2) elucidation of the exact role(s) of these synthetases in repression control of expression of the corresponding biosynthetic operons. Research goals for the coming year include: (a) defining the regulatory region (site) for effector binding for valS, ileS, leuS, and argS, (b) evaluation of post-transcriptional versus transcriptional mode of regulation of formation of these five tRNA synthetases, and (c) in vitro tests of the regulatory effects of the holo-control complexes on synthesis of mRNA/synthetase from DNA templates containing valS, ileS, leuS and argS.